The invention is related to the field of the “medical devices” as defined by the directive 93/42/CE of Jun. 14, 1993 of the European Communities, and notably the “active implantable medical devices” as defined by the directive 90/385/CEE of Jun. 20, 1990 of the European Communities. This definition in particular includes the implants that continuously monitor the cardiac rhythm and deliver if necessary to the heart electrical pulses of stimulation, cardiac resynchronization, cardioversion and/or defibrillation in case of a rhythm disorder detected by the device. It also includes neurological devices, cochlear implants, etc., as well as devices for pH measurement or devices for intracorporeal impedance measurement (such as the measure of the transpulmonary impedance or of the intracardiac impedance).
The invention relates more particularly to those of these devices that implement autonomous implanted capsules and are free from any physical connection to a main implanted (such as the can of a stimulation pulse generator).
These autonomous capsules are called for this reason “leadless capsules” to distinguish them from the electrodes or sensors placed at the distal end of a lead, this lead being traversed throughout its length by one or more conductors connecting by galvanic liaison the electrode or the sensor to a generator connected at the opposite, proximal end, of the lead. Such leadless capsules are, for example, described in U.S. 2007/0088397 A1 and WO 2007/047681 A2 (Nanostim, Inc.) or in U.S. 2006/0136004 A1 (EBR Systems, Inc.).
These leadless capsules can be epicardial capsules, fixed to the outer wall of the heart, or endocardial capsules, fixed to the inside wall of a ventricular or atrial cavity, by a protruding anchoring helical screw, axially extending the body of the capsule and designed to penetrate the heart tissue by screwing to the implantation site. The invention is nevertheless not limited to a particular type of capsule, and is equally applicable to any type of leadless capsule, regardless of its functional purpose.
A leadless capsule includes various electronic circuits, sensors, etc., and a transmitter/receiver for wireless communication for remote data exchange. The signal processing inside the capsule and its remote transmission requires a non-negligible energy compared to the energy resources this capsule can store. However, due to its autonomous nature, the capsule can only use its own resources, such as an energy harvester circuit (by the movement of the capsule), associated with an integrated small buffer battery.
A first type of energy harvester uses a transducer coupled to an inertial mechanism including a mobile mass, called “seismic mass”, oscillating in the capsule according to the movements of the latter, which is subject to forces due to movements of the wall the organ of the patient and to fluid forces from the surrounding medium. The recovered power mainly depends on the excitation frequency of the seismic mass, of the amplitude of the movement and of the value of mass. However, in the case of the environment of the human body, the excitations from the acceleration of the body or organs do not have stable specific frequencies for which the harvesting may be optimized to produce a mechanism resonance. Thus, it is not possible to benefit from a mechanical amplification which would increase the amplitude and allow harvesting of a maximum of inertia energy. Furthermore, the excitation frequencies involved are very low, of the order of 0.5 to 10 Hz for typical pulse frequency of blood flow and 15 to 40 Hz for the movements of the heart walls, which limits performance of the harvester. Finally, the mass value of the seismic mass must remain very low, for fulfilling miniaturization requirements.
Another, non-inertial, type of energy harvester uses variations of the pressure of the fluid surrounding capsule (typically blood medium) to cyclically deform or move a flexible membrane or a bellows coupled to a transducer. The energy that can be harvested depends mainly on the magnitude of the cyclic movement of the diaphragm or bellows operated by the surrounding fluid (which amplitude is necessarily limited for reasons of mechanical reliability), on the frequency of the cyclic movement and on the area of the moving surface (necessarily limited for obvious reasons of miniaturization of the capsule). Again, the pressure variations occur at the heart rate, of the order of 1 to 3 Hz, and therefore only allow applying low frequency to the transducer, thus imposing a limitation of the performance of the energy harvester.
One aspect of the present invention may overcome these limitations by proposing a new type of energy harvester provided with a mechanism increasing the excitation frequency of the transducer, so as to benefit, for a single cycle of external stress, from a plurality of transduction cycles for converting the procured mechanical energy.
On this aspect, U.S. 2011/0140577 A1 describes a ciliated energy harvesting device including two suspended magnets, mounted face-to-face and in opposite poles and each carried by an elastic membrane, together with an inertial mass bearing a third intermediate magnet. The comings and goings of the inertial mass causes successive coupling/decoupling of the suspended magnets at a frequency higher than that of the oscillation of the inertial mass. The oscillation energy of each suspended magnet is harvested by a fixed coil within which the magnet oscillates. While this structure improves the efficiency of energy harvesting, nevertheless it retains the disadvantages described above relating to the dual presence, by nature essential, of a seismic mass and of magnetic means.
Another aspect of the invention may provide such a mechanism that can be used both with a seismic mass inertial harvester, biased by external vibrations and movements of the surrounding environment and with a non-inertial harvester with a membrane or bellows biased by cyclical variations in fluid pressure that surrounds the capsule.
Yet another aspect of the invention may provide such a mechanism that does not implement any magnetic element that would create a risk during MRI or any repetitive shock or mechanical contact which would result in the long term mechanical reliability problems.